We are continuing to investigate the mechanisms involved in murine viral-induced leukemogenesis. The biochemical and biological characteristics of three strains of Friend leukemia virus (FLV) are being studied. The properties of the tissue cultured attenuated virus are being compared to the highly leukemogenic strains to determine what differences exist to account for the attenuation. Infectivity will be tested in various murine hosts. The RNA of each virus strain is being characterized, the size of the cDNA and the degree of base sequence homology among the three strains are being studied. In addition, immunologic studies are in 3rogress to determine the degree of protection against FLV afforded by immunization with various synthetic double-stranded polynucleotide complexes. BIBLIOGRAPHIC REFERENCES: Golde, D. W., Faille, A., Sullivan, A. and Friend, C.: Granulocytic stem cells in Friend leukemia. Cancer Res. 36:115-119, 1976. Reem, G. M. and Friend, C.: Purine and phosphoribosylpyrophosphate synthesis in differentiating murine virus-induced erythroleukemic cells in vitro. J. Cell. Physiol. 88:193-196, 1976.